JPH09230036A - Radar device for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure high responsiveness to a sudden change of relative speed while keeping the resolution high by eliminating the periodic vibration of relative speed by use of LPF having a cut-off frequency changing with the own car speed. SOLUTION: A distance calculating means 7 detects an inter-vehicle distance. A relative speed calculating means 9 calculates the relative speed from the temporal change of the inter-vehicle distance. A car speed sensor 15 detects an own car speed. According to the own car speed, the cut-off frequency of a LPF 11 is decided to conduct LPF processing. Thus, the following effects are obtained. If the speed of a preceding car is very small, the cut-off frequency of the LPF 11 is made smaller than the frequency of the relative speed vibration in order to eliminate the vibration component of the relative speed due to the change of distance from the preceding vehicle as an error. On the other hand, if the speed of the preceding vehicle is substantially equal to the own car speed, the cut-off frequency is determined in proportion to the own car speed, so that the higher the running speed is, the smaller the phase lag of the LPF 11 is, and it is possible to improve the responsiveness to the sudden deceleration of the preceding vehicle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention suppresses a decrease in distance measurement accuracy due to a long pulse wave while constructing a received signal processing device at a low cost by using a wave whose pulse width is longer than a sampling period. The present invention relates to a radar device for a vehicle.

[0002]

2. Description of the Related Art As a conventional vehicle radar device, for example, there is one described in the specification of Japanese Patent Application No. 5-233091. This is a straight line that connects the sampling point and its surroundings or other sampling points by arranging the output obtained by sampling and adding the reflected wave from the target object using a wave whose pulse wave is longer than the sampling period. Is obtained and the time corresponding to the intersection is used for distance calculation. With this configuration, it is possible to obtain a high distance resolution of a sampling period or more without increasing the speed of the circuit.

[0003]

However, such a conventional vehicle radar device has the following problems. That is, in the conventional technology, the reflected waves from the target object are sampled and the outputs obtained by adding are arranged in time series, and the intersection point of the straight line connecting the sampling point and its surroundings or other sambling points is obtained, and the intersection point is dealt with. Since the time to be used is used for distance calculation, a high distance resolution equal to or longer than the sampling period can be obtained, but a slight error occurs in the detection distance. The error itself of the detected distance is a value extremely smaller than the value obtained by converting the sampling period into the distance, and there is no problem in using it as the distance. However, when this detection distance is continuously measured and the relative speed of the target object is calculated by obtaining the amount of change, the error of this detection distance acts differentially, and the error of the relative speed becomes large. I will end up.

Particularly, due to the method of approximating the intersection by approximating with a straight line, other than the error of the detection distance changes due to the positional relationship between the sampling point and the true peak of the addition output, as shown in FIG. In addition, with respect to the true distance to the object, a periodic distance error occurs with the interval of the sampling points being one cycle. FIG. 4 shows a situation in which such a detected distance error is used as it is to calculate a relative speed and the relative speed is applied to an inter-vehicle distance warning. FIG. 4 shows a scene in which the target object is approaching at a constant relative speed as in the case of a stopped vehicle. The calculated relative speed vibrates above and below the true relative speed, as shown in the figure. When the alarm distance of the inter-vehicle distance alarm is calculated using such oscillating relative speed, the value of the alarm distance also vibrates above and below the theoretical value, and as a result, the detected distance is below the alarm distance. The timing (warning timing) varies depending on the vibration width of the warning distance. For example, if an alarm occurs earlier than the original alarm timing,
If the warning is given later than the original warning timing, the effect of preventing a sudden approach to a preceding vehicle or the like is reduced by the warning.

In order to prevent such a variation in the alarm timing due to the error in the relative speed, the relative speed is generally provided with a low-pass filter for removing a high frequency component above a predetermined cutoff frequency (cutoff frequency). , Measures to improve stability will be adopted. Further, in order to further improve the stability of the relative speed, it is desirable to set the cutoff frequency to a value as small as possible.

However, depending on the setting of the low-pass filter, the following problems may occur. FIG.
Shows a scene in which the preceding vehicle drastically decelerates while following the preceding vehicle traveling at a constant vehicle speed, comparing the case where the cutoff frequency of the low-pass filter is set large and the case where it is set small. Is shown. In such a situation, when the preceding vehicle starts to decelerate rapidly, the inter-vehicle distance decreases,
An alarm is issued when the relative speed increases and the alarm distance further increases and exceeds the detection distance. However, the characteristic of the low-pass filter is that there is a problem called phase lag in which the change in the output value is delayed with respect to the change in the input value, and the degree of delay differs depending on the cutoff frequency.
The smaller the cutoff frequency is set, the larger the delay becomes. Therefore, in the scene of sudden deceleration of the preceding vehicle as shown in FIG. 5, if the cutoff frequency is set too small, the delay of the change in the relative speed becomes large and the increase of the warning distance also delays, so that the warning timing is delayed. As a result, the effect of preventing a sudden approach to the preceding vehicle due to the alarm becomes small. Thus, when using a low-pass filter,
There is a trade-off relationship between ensuring the stability by suppressing the variation of the alarm timing and reducing the delay of the alarm timing, and it is impossible to make both of them compatible.

The present invention has been made by paying attention to such a conventional problem, and uses a low-pass filter having a cutoff frequency that changes according to the sampling interval and the vehicle speed at that time, to determine the relative speed. The purpose is to solve the above problems by eliminating periodic vibrations.

[0008]

In order to achieve the above object, in the invention according to claim 1, a pulse of an electromagnetic wave, light, or a sound wave is sent, and the sent electromagnetic wave, light, or a sound wave is reflected by a target object. The waves are sampled and added, the received reflected waves are sampled, and the outputs that are added are arranged in a time series to find the intersection of the straight line connecting the sampling point and its surroundings or other sampling points. In a vehicle radar device that uses corresponding times for distance calculation, a means for calculating relative speed from continuously detected distances, and a high-frequency noise component having a cutoff frequency higher than a certain cutoff frequency of the relative speed calculated by the relative speed calculation means. And a cutoff frequency changing means for changing the cutoff frequency. As a result, it is possible to stably remove the vibration of the relative speed having the cycle of the sampling interval due to the calculation method of the detection distance, and to cope with the sudden change of the relative speed such as the sudden deceleration scene of the preceding vehicle during the following running. It is possible to achieve the two contradictory performances of ensuring high responsiveness. As described in claim 2, the cutoff frequency may be proportional to the traveling vehicle speed as a means for varying the cutoff frequency.

[0009]

Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a vehicle radar device 12 according to an embodiment of the present invention. First, the configuration will be described. In FIG. 1, 3 is a radar main body, 1 is a pulse signal sending means, 2 is a reflected pulse signal receiving means, 4 is a control means for controlling the sending timing of pulse signals, and 6 is a phase sampling addition. Means, 8 is peak detection means of sampling addition signal, 7 is distance calculation means using a microcomputer or the like, 9 is relative speed calculation means for calculating relative speed from distance, and 15 is the current traveling speed of the own vehicle (own vehicle speed). Vf) is a vehicle speed sensor, and 11 is a low-pass filter means for applying a low-pass filter having a cutoff frequency corresponding to the vehicle speed to the relative speed.

FIG. 2 shows the configuration of a system in which the vehicle radar device 12 of the present embodiment shown in FIG. 1 is applied to an inter-vehicle distance warning device. Inter-vehicle distance R and relative speed V with the preceding vehicle
The vehicle radar device 12 that detects r, the vehicle speed sensor 15 that detects the own vehicle speed Vf, the inter-vehicle distance R from the radar device 12, the relative speed Vr, and the own vehicle speed Vf from the vehicle speed sensor 15.
The information processing circuit 13 determines whether or not to generate an alarm according to the above, and generates an alarm signal, and an alarm generation device 14 that receives the alarm signal and generates an alarm.

Next, the operation will be described. The radar device 12 detects the distance R to the front reflector and the relative speed Vr of the preceding vehicle, and the vehicle speed sensor 15 detects the own vehicle speed Vf. These three types of signal values are input to the information processing circuit 13, and in the information processing circuit 13, the relative speed Vr and the vehicle speed V
The alarm distance Rs is calculated according to f.

After that, by comparing the warning distance Rs with the inter-vehicle distance R, the risk of a rear-end collision with the preceding vehicle is judged, and an alarm signal is output so as to issue an alarm when the rear-end collision risk is high. In response to this alarm signal, the alarm generator 14 issues an alarm. The method of generating this alarm is, for example,
Visual presentation by alarm lamps, etc., and auditory presentation such as generation of alarm sounds.

The detailed operation of the radar device 12 will be described with reference to FIG. FIG. 6 shows a schematic processing flow. First, in step 101, the inter-vehicle distance R is detected.
The method of detecting the inter-vehicle distance R here is similar to the method described in the conventional example, in the distance calculating means 7, the peak value of the sampling addition output and the front and rear thereof are connected by a straight line to obtain an intersection point, and the reflected wave is received. As the time, the time T required from the transmission of the distance measurement wave to the reception of the reflected wave from the distance measurement target object is calculated. Furthermore, the inter-vehicle distance R from the required time T to the object is detected. If there is no inter-vehicle distance R this time, the processing of this time ends, but if there is inter-vehicle distance R, the process proceeds to step 103 and thereafter.

In step 103, the relative speed Vr0 is calculated by obtaining the time change of the inter-vehicle distance R. As the calculation method, a least square method having high stability and viscosity is used. However, for calculation, for example, the past three data are required in addition to the current inter-vehicle distance, and if the past inter-vehicle distance data are not available, the relative speed cannot be calculated. Further, even if the past inter-vehicle distance data is available, if the inter-vehicle distance data this time is significantly different from the previous inter-vehicle distance data (for example, 100 mse
(When changing by 10 m or more during the measurement cycle dt of c)
Since there is a high possibility that a target different from the previous one has begun to be detected, the distance data of the past three times recorded so far will be reset and a new memory will be newly started from this time. In this way, when the relative speed Vr0 cannot be calculated, the current processing ends in step 104 and returns to the beginning.

The formula for calculating the relative velocity Vr0 is obtained by, for example, the least square method, and the following formula 1 is used.

[0016]

(Equation 1) Here, R ₀ : current inter-vehicle distance, R _{1 to} R ₃ : past 1 to
Inter-vehicle distance three cycles before, dt: measurement cycle time question.

When the relative speed Vr0 can be calculated, the routine proceeds to step 105, where the current own vehicle speed Vf is read. Further, in step 106, the cutoff frequency fc of the low-pass filter 11 is determined according to the vehicle speed Vf, and low-pass filter processing is performed. The specific processing here is as follows.

(Low-pass filter processing) First, the vehicle speed V
Cutoff frequency f of the low-pass filter 11 according to f
c is determined by the following Equation 2.

[0019]

(Equation 2) Here, L ₀ is a distance corresponding to the interval between sampling points, which is the sampling interval shown in FIG. For example,
When the sampling period is set to 66.7 μs,
This sampling interval L ₀ is 10 m. K is a proportional constant and may be a constant value between 0 and 1. By using this equation 2, the cutoff frequency f
c is set in proportion to the vehicle speed Vf.

Next, each parameter of the low pass filter 11 corresponding to the value of the cutoff frequency is calculated. When a second-order low-pass filter L (s) such as the following expression 3 is used, each parameter of the low-pass filter may be set as in the following expression 4.

[0021]

(Equation 3)

[0022]

(Equation 4) here,

[0023]

(Equation 5) It is. Each coefficient for performing the low-pass filter processing by digital processing on each of the obtained parameters a _{0 to} b _{0 of} the low-pass filter 11 is calculated by the following Expression 6.

[0024]

(Equation 6) Here, dt is a cycle in which distance detection and relative speed calculation are performed.

The calculated value of the relative speed Vr0 is subjected to the low-pass filter processing as shown in Expression 7 having each coefficient calculated by Expression 6 to obtain the relative speed correction value Vr0L.

[0026]

[Formula 7] Here, Vr0 to Vr2: relative velocities of the present and past two cycles not subjected to low-pass filter processing, Vr1L to Vr.
2L: Relative speed for the past two cycles after low-pass filter processing.

Further, this low-pass filter 11 has the formula 7
As can be seen from the above, since the value of the relative speed correction value after the low pass filter processing for the past two cycles is required, the expression 7 is used after the third cycle from the start of detection. If there is no past relative velocity data in the two cycles from the start of detection, the value before the low-pass filter processing may be used as it is.

Thereafter, in step 107, the information processing circuit 1
3, the inter-vehicle distance R and the relative speed Vr0L are output, and the processing of this time is ended.

The information processing circuit 13 makes an alarm judgment as to whether or not an alarm should be issued. The details will be described below. (Alarm Judgment Processing) FIG. 7 shows a processing flow of alarm judgment. First, in step 121, each data such as the inter-vehicle distance R and the relative speed Vr0L detected by the radar device 12 and the own vehicle speed Vf detected by the vehicle speed sensor 15 are read. Next, in step 122, the warning distance is calculated.
As the warning distance, a warning distance Rs1 for the primary warning and a warning distance Rs2 for the secondary warning are calculated. This alarm distance is calculated based on the following two expressions, Expression 8 and Expression 9.

[0030]

(Equation 8)

[0031]

[Equation 9]

In step 123, the inter-vehicle distance R and the primary warning distance Rs1 are compared, and the risk of a rear-end collision is determined by the following expression 10.

[0033]

(Equation 10) If this expression 10 is satisfied, it means that the distance is less than the primary alarm distance, and the primary alarm or the secondary alarm is generated in step 124 and the subsequent steps. If the expression 10 is not satisfied, the alarm is not issued and the process returns to the next process.

In step 124, the secondary warning distance Rs2 and the vehicle interrogation distance R are further compared, and the risk of a rear-end collision is determined by the following equation 11.

[0035]

[Equation 11] If this expression 11 is satisfied, it means that the inter-vehicle distance R is equal to or less than the secondary warning distance Rs2, and step 12
Proceed to step 5 to generate a secondary alarm. Secondary alarm distance Rs2
If the inter-vehicle distance R is larger than that, the routine proceeds to step 127, where a primary alarm is issued. In the case of the primary alarm, in step 127, from the current time Tn and the alarm generation time point TF1,
Alarm time △ t
If it is within t, an alarm sound for the primary alarm is generated in step 128, and a command value is output to the alarm generation device 14 so as to turn on the alarm lamp for the primary alarm in step 129.
If the alarm time Δt is exceeded, the alarm sound for the primary alarm is stopped in step 130, and only the alarm lamp is turned on. In step 125, an alarm sound for a secondary alarm is generated, and in step 126, a command value is output to the alarm generator 14 so as to turn on the alarm lamp for the secondary alarm. 1
After both the secondary and secondary alarms are issued, return to the beginning,
Repeat the next process.

By the above processing, the cutoff frequency f proportional to the relative vehicle speed Vf with respect to the relative speed is obtained.
Since the low-pass filter process having c can be performed, the following effects can be obtained. FIG. 8 shows the vehicle speed Vf
And the preceding vehicle speed Va on each of the XY axes, and the effect of making the cutoff frequency proportional to the own vehicle speed Vf in this figure will be described. First, when the preceding vehicle speed Va is very small as in the region 1 (this indicates, for example, when approaching a stopped vehicle), the vibration of the relative speed Vr due to the distance change with respect to the preceding vehicle is almost equal to the own vehicle speed Vf at the sampling interval. It has a frequency fn≈Vf / L0 divided by L0. Therefore, in order to remove this vibration component as an error, the cutoff frequency fc of the low-pass filter 11 may be made smaller than the frequency fn of the relative velocity vibration. The cutoff frequency fc of the low-pass filter 11 is always set to be smaller than the frequency fn of the relative speed vibration according to the equation 2, and the stability of the relative speed can be secured regardless of the own vehicle speed Vf.

On the other hand, when the preceding vehicle speed Va is almost equal to the own vehicle speed Vf as in the area 2, the responsiveness to the rapid deceleration of the preceding vehicle from the following traveling state is required. In particular, responsiveness at high speed is important, and it is desirable that the delay in the change in relative speed be as small as possible. According to the present embodiment, since the cutoff frequency fc is determined in proportion to the vehicle speed Vf, the phase delay of the low pass filter 11 becomes smaller as the vehicle travels at higher speeds, and the responsiveness of the preceding vehicle to sudden deceleration is improved.

As described above, in the embodiment, the vibration of the relative speed having the cycle of the sampling interval caused by the method of calculating the inter-vehicle distance R is stably removed, and the preceding vehicle suddenly decelerates during follow-up running. It is possible to achieve the two contradictory performances of ensuring high responsiveness to such a sudden change in relative speed. As a result, it is possible to reduce the variation in the alarm timing and to issue the alarm at an appropriate timing without delay.

The embodiment of the present invention has been described in detail above with reference to the drawings. However, the specific configuration is not limited to this embodiment, and design changes and the like without departing from the gist of the present invention. Even if it is included in the present invention.

[0040]

As described above, according to the present invention, the cutoff frequency of the low-pass filter is configured to be changed according to the sampling interval and the vehicle speed at that time. The periodic vibration of the relative speed with the cycle of the sampling interval is removed to obtain a high distance resolution without increasing the speed of the circuit configuration, and the relative speed of the relative speed such as the sudden deceleration scene of the preceding vehicle during follow-up running is obtained. To ensure high responsiveness to sudden changes,
It is possible to make the two contradictory performances compatible with each other.

[Brief description of drawings]

FIG. 1 is a system block diagram of a vehicle radar device according to an embodiment of the present invention.

FIG. 2 is a system block diagram when an embodiment of the present invention is applied to an inter-vehicle distance warning device.

FIG. 3 is an explanatory diagram for explaining a conventional problem.

FIG. 4 is an explanatory diagram for explaining a conventional problem.

FIG. 5 is an explanatory diagram for explaining a conventional problem.

FIG. 6 is a flowchart for explaining the operation of the embodiment.

FIG. 7 is a flowchart for explaining the operation of the embodiment.

FIG. 8 is an explanatory diagram for explaining an effect of the embodiment.

[Explanation of symbols]

 1 pulse signal sending means 2 reflected pulse signal receiving means 3 radar main body 4 control means 6 phase sampling adding means 7 distance calculating means 8 peak detecting means 9 relative speed calculating means 11 low-pass filter means 15 vehicle speed sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location G01S 17/08 G01S 13/93 Z

Claims (2)

[Claims] 1. An electromagnetic wave, light or sound wave pulse is sent, reflected waves of the sent electromagnetic wave, light or sound wave from a target object are sampled and added, and a received reflected wave is sampled and added to obtain an output. Arranged in time series, the intersection of the straight line connecting the sampling point and the sampling points and the points before and after it or other sampling points is obtained, and the time corresponding to this intersection is continuously detected in the vehicle radar device that uses the distance calculation. Means for calculating the relative speed from the distance, a low frequency pass filter means for calculating the relative speed correction value by removing the high frequency noise component above a certain cutoff frequency of the relative speed calculation value by the relative speed calculation means, A vehicle radar device comprising cutoff frequency varying means for varying the cutoff frequency. 2. The vehicle radar device according to claim 1, wherein the cutoff frequency is made proportional to a traveling vehicle speed as a means for varying the cutoff frequency.